The present invention relates to a method and noise dosimeter for measuring a user""s exposure to noise when using appliances employing earphones and headsets.
Evidence suggests that individuals spending significant time using appliances with earphones or headsets may be exposed to excessive acoustical noise doses. Unfortunately, monitoring appliances for noise emissions is typically not done and when it is, it is usually done only after a significant number of users suffer hearing loss. The end result can be significant compensation claims.
To-date, two methods have been used to measure a user""s exposure to noise when using an appliance, namely a direct method and an indirect method. In the direct method, each subject to be tested for noise exposure is fitted with a probe microphone inserted in the subject""s ear canal. As will be appreciated, this method is intrusive and requires the services of a specialist and the use of specialized tools. As a result, only a limited number of subjects can be tested and only for a limited amount of time.
In the indirect method, the earphones or headset of the appliance to be monitored for noise emissions is placed on an artificial head that measures the acoustical pressure applied to its ear. Unfortunately, these artificial heads are expensive. Also, the artificial heads do not take volume level changes, controlled by users, into account. Accordingly, improvements to appliance noise monitoring are desired.
It is therefore an object of the present invention to provide a novel method and noise dosimeter for measuring a user""s exposure to noise when using appliances employing earphones or headsets.
According to one aspect of the present invention there is provided a noise dosimeter for an appliance including a speaker to broadcast signals comprising:
a filter receiving signals to be broadcast by said speaker and having a transfer function generally modeling the frequency response of said appliance to provide output approximating noise appearing at said speaker;
signal processing circuitry to process the output of said filter; and
an accumulator to accumulate the output of the signal processing circuitry, the value in said accumulator representing a user""s exposure to noise when using said appliance.
Preferably, the noise dosimeter includes sampling period circuitry scaling the output of the accumulator to provide a value representing the user""s exposure to noise over a specified period of time. In this case, the accumulator is responsive to a reset signal to reset the value therein after expiry of the specified period of time. It is also preferred that the filter is a digital filter applying A-weighted free-field corrections to the signals and that the signal processing circuitry includes a squaring function squaring the output of the digital filter. Furthermore, it is preferred that the signal processing circuitry also includes multiplier means to scale the signals received by the digital filter in accordance with a volume setting.
The value held by the accumulator can be converted into units of decibels, and forwarded to a display for visual presentation, and/or to a private branch exchange or computer for logging.
According to another aspect of the present invention there is provided in a telephone device including a digital to analog converter receiving an input PCM data stream, an amplifier amplifying the analog output of said digital to analog converter, a headset speaker broadcasting the amplified analog output, a microphone receiving audio input, and an analog to digital converter receiving the microphone output and generating an output PCM data stream, a noise dosimeter comprising:
a first multiplier receiving said input PCM data stream and a volume setting value;
a second multiplier receiving said output PCM data stream and a sidetone volume setting value, said first and second multipliers scaling said PCM data streams by said volume setting values;
a summing circuit to sum the outputs of said first and second multipliers;
a digital filter receiving the output of said summing circuit and having a transfer function generally modeling the frequency response of said digital to analog converter, amplifier and speaker to provide output approximating noise appearing at said speaker;
signal processing circuitry to process the output of said digital filter; and
an accumulator to accumulate the output of the signal processing circuitry, the value in said accumulator representing a user""s exposure to noise when using said telephone device.
According to a further aspect of the present invention there is provided a method for measuring a user""s exposure to noise when using an appliance having a speaker broadcasting signals comprising the step of:
monitoring the signals to be broadcast by said speaker;
filtering the monitored signals to generate output approximating noise appearing at said speaker;
processing and accumulating the output to generate a value representing a user""s exposure to noise appearing at said speaker over a specified period of time.
The present invention provides advantages in that a user""s exposure to noise when using the appliance is monitored allowing excess noise exposure to be determined quickly so that steps can be taken to inhibit user hearing loss.